METHOXYCHLOR

Please Note: The main source of information for this fact sheet is EPA's Integrated Risk Information System (IRIS), which contains information on oral chronic toxicity of methoxychlor and the RfD. Other secondary sources include the Hazardous Substances Data Bank (HSDB), a database of summaries of peer-reviewed literature, and the Registry of Toxic Effects of Chemical Substances (RTECS), a database of toxic effects that are not peer reviewed.

Environmental/Occupational Exposure

* The most probable route of exposure to methoxychlor would be from inhalation or dermal contact by workers involved in the manufacture, handling, or application of this compound. (1)

* Individuals could be exposed during home use of this insecticide or by ingestion of food or drinking water contaminated with methoxychlor. (1)

Assessing Personal Exposure

* No information was located regarding the measurement of personal exposure to methoxychlor.

Health Hazard Information

Acute Effects:

* Information on the acute (short-term) systemic effects of methoxychlor in humans is not available.

* Dermal contact with methoxychlor is slightly irritating to skin in humans. (2)

* Depression of the central nervous system, progressive weakness, trembling, convulsions, diarrhea, and possibly death are symptoms reported in animals acutely exposed to methoxychlor. (3,4)

* In a study of rats exposed to methoxychlor orally, changes in the kidney, liver, and heart muscle were reported. Loss of body weight and growth retardation have also been observed. (4)

* Tests involving acute exposure of animals, such as the LD50 test in rats, mice, and rabbits, have demonstrated methoxychlor to have low to moderate acute toxicity from oral or dermal exposure. (5)

Chronic Effects (Noncancer):

* Information on the chronic (long-term) effects of methoxychlor in humans is not available. However, exposure to chemically related organochlorine pesticides has caused liver and kidney damage in humans. (1)

* Chronic exposure of rats and monkeys to methoxychlor by gavage (placing the chemical experimentally in their stomachs) has been observed to damage the liver and small intestine. (7)

* In dogs orally exposed to methoxychlor, weight loss, blood effects, and intestinal congestion were observed; kidney injury was observed in swine. (1,7)

* EPA has not established an RfC for methoxychlor. (6)

* The RfD for methoxychlor is 0.005 mg/kg/d based on the excessive loss of litters in rabbits. (6)

* EPA has low confidence in the critical study because no conclusions could be made relative to the maternal or developmental toxicity of methoxychlor due to the total loss of litters in the high-dose group and the small number of litters available for evaluation in the mid-dose group; low confidence in the database because of the lack of definitive chronic toxicity; and, consequently, low confidence in the RfD.

* EPA's Office of Air Quality Planning and Standards, for a hazard ranking under Section 112(g) of the Clean Air Act Amendments, has evaluated methoxychlor for chronic toxicity and has given it a composite score of 8 (scores range from 1 to 100, with 100 being the most toxic). These scores are nonlinear and are the product of two ratings: a rating based on the minimal-effect-dose and a rating based on the type of effect. (8)

Reproductive/Developmental Effects:

* No information is available on the reproductive or developmental effects of methoxychlor in humans.

* In rabbits orally exposed to methoxychlor, excessive loss of litters (abortions) was observed. (6)

* Long-term oral exposure of rats to methoxychlor has been reported to reduce maternal fertility and increase fetotoxicity, as well as to reduce fertility in the offspring. (6)

* Skeletal effects have been observed in the offspring of rats exposed to methoxychlor by gavage (experimentally placing the chemical in the stomach). (6)

Cancer Risk:

* No human studies are available on the carcinogenicity of methoxychlor.

* A number of animal cancer studies have been carried out on methoxychlor, with both positive and negative results. EPA considers the data to be inconclusive, based on problems with the data and interpretation of the results. (4,6)

* EPA has classified methoxychlor as a Group D, not classifiable as to human carcinogenicity, based on the fact that human data are unavailable and animal evidence is inconclusive. (6)

Physical Properties

* The chemical formula for methoxychlor is C6H15Cl3O2, and its molecular weight is 346.65 g/mol. (4)

* Methoxychlor occurs as white to pale yellow dimorphic crystals that are practically insoluble in water. (1,2,4)

* Methoxychlor has a slightly fruity odor; the odor threshold has not been established. (3)

* The log octanol/water partition coefficient (log Kow) for methoxychlor is about 3.05 to 4.30. (4)

Uses

* Methoxychlor is used as an insecticide (effective against biting flies, houseflies, and mosquito larvae) and is considered to be an excellent replacement for DDT. (1,3)

* Methoxychlor is also used against the elm bark-beetle vectors of Dutch elm disease. (3)

* In veterinary practices, methoxychlor is used as an ectoparasiticide (a medicine used to kill parasites that live on the exterior of their host). (2)

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